Analytical investigations of seismic responses for reinforced concrete bridge columns subjected to strong near-fault ground motion

Strong near-fault ground motion, usually caused by the fault-rupture and characterized by a pulse-like velocity- wave form, often causes dramatic instantaneous seismic energy (Jadhav and Jangid 2006). Some reinforced concrete (RC) bridge columns, even those built according to ductile design principles, were damaged in the 1999 Chi-Chi earthquake. Thus, it is very important to evaluate the seismic response of a RC bridge column to improve its seismic design and prevent future damage. Nonlinear time history analysis using step-by-step integration is capable of tracing the dynamic response of a structure during the entire vibration period and is able to accommodate the pulsing wave form. However, the accuracy of the numerical results is very sensitive to the modeling of the nonlinear load-deformation relationship of the structural member. FEMA 273 and ATC-40 provide the modeling parameters for structural nonlinear analyses of RC beams and RC columns. They use three parameters to define the plastic rotation angles and a residual strength ratio to describe the nonlinear load- deformation relationship of an RC member. Structural nonlinear analyses are performed based on these parameters. This method provides a convenient way to obtain the nonlinear seismic responses of RC structures. However, the accuracy of the numerical solutions might be further improved. For this purpose, results from a previous study on modeling of the static pushover analyses for RC bridge columns (Sung et al. 2005) is adopted for the nonlinear time history analysis presented herein to evaluate the structural responses excited by a near-fault ground motion. To ensure the reliability of this approach, the numerical results were compared to experimental results. The results confirm that the proposed approach is valid.     

混杂纤维高强高性能混凝土抗冲击性能数值仿真

采用有限元软件ANSYS/LS-DYNA分析平台,对钢纤维、聚丙烯纤维等混杂纤维混凝土(HFRHSC)试件在强动载作用下力学相响应进行了仿真分析,主要针对混杂纤维混凝土的霍普金森压杆冲击试验过程进行数值仿真。采用了HJC(Holmquist-Johnson-Cook)破坏模型,针对混凝土材料冲击损伤破坏的本构模型来计算动态冲击作用下混凝土材料的变形问题。表明了试件内部应力趋于均匀前,经历初始状态的应力震荡;相同的冲击速度下,HFRHSC试件各个时刻的破坏程度轻于没有参加任何纤维的的基本混凝土试件,基本验证了混杂纤维对混凝土力学性能的改良效用。     

反射技术推算混凝土支承桩竖向允许承载力的方法

用地震波反射技术估算混凝土支承桩允许的纵向支承能力,并用实例说明了其工作原理,用此法测试了500根支承桩,均取得了满意的效果.     

Seismic fragility analysis of composite frame structure based on performance

Steel-concrete composite structures that share the advantages of both steel structure and concrete structure have been developed rapidly and used widely. It has been a popular structure in high-rise buildings in recent years. Although more and more composite structures have been used in earthquake area, only a few literatures about fragility analysis of this type of structure are available. In this paper, a fragility analysis method based on performance is proposed, in which both the uncertainty due to vari...     

静压预应力混凝土管桩土塞效应试验研究

对淤泥质黏土互层以及粉土两种土层条件下静压预应力混凝土管桩的土塞效应进行了试验研究。现场及室内试验结果显示,管桩径厚比越大、土层条件越为坚硬则形成的土塞相对高度越大。上硬下软的土层分布易形成闭塞现象,而上软下硬的情况则易导致土塞的滑动。沉桩过程中,管壁端阻与静力触探锥尖阻力具有极为相似的变化规律,两者比值不随土塞高度变化率及沉桩深度的变化而改变。管壁端阻与锥尖阻力的相关性与土层条件密切相关,对于淤泥质黏土和粉土而言,两者比值分别为0.59和0.81。土塞的分层与地基土层分布基本一致,且分层界面为向上凸起的曲面。土塞形成过程中挤密效应是显著的,黏聚力则因扰动的影响有不同程度的降低。直剪试验显示,土塞抗剪强度的时效性是显著的。粉土中预应力混凝土管桩有效土塞高度约为5～6倍桩径,为整个土塞高度的70%;而淤泥质黏土中有效土塞高度大于4倍桩径。试验结果与已有的研究结果较为接近     

方钢管混凝土柱-钢梁平面框架耐火性能研究

建立了局部火灾下多层多跨矩形钢管混凝土柱-钢梁平面框架温度场和力学性能分析的有限元模型。在考虑楼板影响的基础上,研究了保护层厚度不同时钢管混凝土框架结构的温度场分布规律。研究了不同受火工况条件下钢管混凝土框架结构的变形和破坏规律、耐火极限状态、受火梁的内力状态以及结构耐火极限的规律。分析表明,梁保护层厚度影响钢梁温度分布形式;火灾下,框架结构发生了受火梁的整体屈曲破坏。     

耗能-隔震柔性底层钢管混凝土-钢筋混凝土组合框架的实验研究

本文用钢管混凝土柱作为结构底层耗能柱、用承重墙和隔震器控制结构底层倒塌破坏,从而提出了一种新的耗能-隔震柔性底层结构体系。通过本文12根钢管混凝土柱和文献[7]中7根钢管混凝土柱的低周疲劳实验,初步确定了钢管混凝土柱地震损伤模型的参数;通过两个钢管混凝土-钢筋混凝土三层框架模型和一个纯钢筋混凝土三层框架模型的拟动力实验,研究和比较了两类结构体系的地震损伤。     

基于ANSYS混凝土重力坝稳定动力响应分析

为了研究在静力作用下安全稳定及应力变形规律以及地震动持作用下重力坝的动力响应,应用时程分析法通过有限元数值模拟方法对混凝土重力坝进行三维模型计算。结果表明：静力作用下以及地震动持作用下重力坝的坝趾和坝踵部位应力均较为集中,坝踵处最大,与其它重力坝的其它部位比较,左坝底部的应力集中,特别是在左坝底部与水压、基岩的交界地带,引起了坝体的滑移,因此,建议对此处进行加固处理;重力坝坝体的最大幅值通常出现在坝顶,而且动力放大效应很强。坝体最大振幅一般发生在坝顶,其动态放大作用较大。由于坝顶突然发生的突然变化,导致了坝顶的横向开裂,必须采用相应的工程措施来降低坝顶的荷载,从而使其具有更好的结构刚度。     

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